Surfactant nebulisation : lung function, surfactant distribution and pulmonary blood flow distribution in lung lavaged rabbits

Surfactant nebulisation is a promising alternative to surfactant instillation in newborns with the respiratory distress syndrome. Although less surfactant is deposited in the lung, it improves gas exchange, probably due to a superior distribution. We hypothesize that a more uniform distribution of nebulised surfactant results in a more uniform pulmonary blood flow and consequently a more efficient gas exchange. We asked whether the pulmonary blood flow changes after surfactant replacement, and to what extent pulmonary blood flow is influenced by the amount of surfactant deposition. Furthermore, we investigated whether sufficient nebulised surfactant is deposited in the lungs to achieve a sustained improvement in lung function. Surfactant was nebulised or instilled, or saline was nebulised, in 18 lung-lavaged rabbits. After 2 h the rabbits were weaned from mechanical ventilation to continuous positive airway pressure, 40% oxygen. We measured blood gasses, dynamic lung compliance, surfactant distribution using 99m technetium nanocoll label, and the pulmonary blood flow distribution, using microspheres. Partial pressure of oxygen in arterial blood and lung compliance were significantly higher after surfactant nebulisation than after saline nebulisation. Surfactant instillation gave a superior effect with respect to these variables. Nebulised surfactant was distributed more uniformly over the lungs than instilled surfactant. Although pulmonary blood flow changed over time, it remained uniformly distributed following both modes of surfactant treatment. Surfactant deposition was neither strongly related to pulmonary blood flow nor strongly related to the change in blood flow. Although nebulised surfactant is uniformly distributed, we can provide no evidence that this results in a more uniform pulmonary blood flow distribution. Therefore, other than a superior surfactant distribution, no additional reason was found for the efficient gas exchange after nebulisation.